Image forming apparatus

ABSTRACT

A multi-function printer includes a fuser unit which includes a heat roller and a pressure roller; a duct which is formed in a long shape in a direction along an axis of the heat roller, is disposed in the vicinity of the fuser unit along the axis of the heat roller, and is exhausted by an exhaust fan which is provided on one end side in a long-side direction; an exhaust port which is opened to a first side wall of the fuser unit side of the duct and causes the fuser unit and the duct to communicate with each other; and a planar filter which is attached to an inner wall surface of the duct and in which the surface of the filter is an irregular surface on which ditches and convex portions extending in a direction inclined to the long-side direction of the duct are alternately disposed in the long-side direction of the duct.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrophotographic image formingapparatus.

2. Description of the Related Art

In an electrophotographic image forming apparatus, it is known that aplurality of kinds of chemical substances are discharged from an imageforming apparatus during image forming. For example, as a representativeof the discharged chemical substances, there is ozone generated when aphotosensitive drum is charged, or toner dust generated duringdeveloping or fusing. In the related art, in order to not allow thegenerated chemical substances to be discharged outside the image formingapparatus, for example, a measure of providing a filter or the like isperformed.

For example, in a volatile chemical substance collection device of anelectronic apparatus disclosed in Japanese Patent Unexamined PublicationNo. 2009-282455, an electric field is generated in an atmosphere from anelectric field generating collection member in an exhaust duct providedabove a fuser unit, and volatile organic compounds (VOC) included in theatmosphere are drawn to the surface of the electronic field generatingcollection member by the operation of the electric field so as to becollected.

In an image forming apparatus disclosed in Japanese Patent UnexaminedPublication No. 2011-180235, a duct which includes a take-in port fortaking-in minute particles generated from a heat roller inside a fusingdevice is provided in the vicinity of the fusing device. An exhaust fanwhich generates a flow of air from the take-in port toward an outlet isprovided in an expansion portion of the duct, and a first filter memberis provided on the upstream side of the exhaust fan. The first filtermember captures ultrafine particles (for example, siloxane) generatedfrom a rubber layer configuring the fusing device. A shutter whichcloses a gap between the first filter member and the expansion portionis provided, and a control portion of the image forming apparatusswitches a state where the shutter closes a first filter portion and astate where the shutter does not close the first filter portionaccording to a predetermined initial burst condition.

In an odor removing device of a multi-function image forming apparatusdisclosed in Japanese Patent Unexamined Publication No. 2011-180283, aplurality of air passage portions for introducing air inside a housingare formed on a housing bottom portion. Each air passage portion is acylindrical body in which an inner diameter of the upper portion sideinside the housing is smaller than an inner diameter of the housingbottom portion, and an ozone decomposition filter including an ozonedecomposition catalyst is disposed on an inner diameter surface of thecylindrical body. A waste liquid absorbing material is disposed on thebottom portion inside the housing, a deodorizing absorbent is disposedon an upper cover inside the housing, and an exhaust port of the airpassing through a portion between the waste liquid absorbing materialand the deodorizing absorbent is provided on the side surface of thehousing.

However, in recent years, according to enhancement in consciousness withrespect to worldwide environment protection, minute particles (forexample, ultrafine particles (UFP) having a particle diameter less thanor equal to 100 nm) different from ozone or the like occurring from anelectrophotogrpahic image forming apparatus have become a problem.

As a structure which captures the ultrafine particles, for example, likethe electronic apparatus disclosed in Japanese Patent UnexaminedPublication No. 2009-282455, when the volatile chemical substancecollection device which draws volatile organic compounds to the surfaceof the electric field generating collection member and collects thecompounds is additionally provided, there is a problem in that thestructure becomes complicated.

For example, as the image forming apparatus disclosed in Japanese PatentUnexamined Publication No. 2011-180235, when the structure in which thefirst filter member capable of capturing minute particles is provided onthe upstream side of the exhaust fan and the exhaust gas permeates thefirst filter member is provided, the first filter member increasesresistance when the air is transported, and thus, exhaust efficiency isdecreased and the temperature inside the housing is increased.Accordingly, the output of the exhaust fan should be increased, andthus, there is a problem that noise is generated and running cost isincreased.

For example, as the multi-function image forming apparatus disclosed inJapanese Patent Unexamined Publication No. 2011-180283, when theplurality of (for example, two in Japanese Patent Unexamined PublicationNo. 2011-180283) exclusive odor removing devices are additionallyprovided, the structure becomes complicated and, there is a problem thata cost of the apparatus is also increased.

The present invention is made for solving the above-described problemsin the related art, and an object thereof is to provide an image formingapparatus which decreases amounts of emission of ultrafine particles andsuppresses an increase of output of the exhaust fan by a simplestructure.

SUMMARY OF THE INVENTION

According to the present invention, there is provided an image formingapparatus including: a fuser unit which includes a heat roller and apressure roller which heats and pressurizes a sheet on which an unfusedtoner image is carried and fuses the unfused toner image on the sheet; aduct which is formed in a long shape in a direction along an axis of theheat roller, is disposed in the vicinity of the fuser unit along theaxis of the heat roller, and is exhausted by an exhaust fan which isprovided on one end side in a long-side direction; an exhaust port whichis opened to a first side wall of the fuser unit side of the duct andcauses the fuser unit and the duct to communicate with each other; and aplanar filter which is attached to an inner wall surface of the duct, inwhich the surface of the filter is an irregular surface on which ditchesand convex portions extending in a direction inclined to the long-sidedirection of the duct are alternately disposed in the long-sidedirection of the duct.

According to the present invention, it is possible to decrease an amountof emission of ultrafine particles and suppress an increase in output ofthe exhaust fan, by a simple structure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a longitudinal cross-sectional view of a multi-functionprinter of the present embodiment;

FIG. 2 is a perspective view when a first side wall of themulti-function printer shown in FIG. 1 is viewed from a fuser unitcontainer side;

FIG. 3 is a perspective view when FIG. 2 is cut at an approximatelycenter position in a long-side direction of a heat roller;

FIG. 4 is a perspective view when FIG. 3 is viewed from the lowerportion of a duct side;

FIG. 5 is a perspective view when an exhaust port of a first side wallis viewed from the upper portion in a state where a ceiling surface ofthe duct of the multi-function printer of the present embodiment is notshown;

FIG. 6 is a perspective view of a filter in the multi-function printerof the present embodiment;

FIG. 7 is a perspective view of a thru-beam type filter of themulti-function printer of the present embodiment; and

FIG. 8 is a perspective view of a filter in a multi-function printer ofanother embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment (hereinafter, referred to as the “presentembodiment”) of an image forming apparatus according to the presentinvention will be described with reference to the drawings. In thepresent embodiment below, as an example of the image forming apparatusaccording to the present invention, an electrophotographicmulti-function printer will be described. However, the image formingapparatus according to the present invention is not limited to themulti-function printer, and for example, may be also applied to a copieror printer.

FIG. 1 is a longitudinal cross-sectional view of multi-function printer11 of the present embodiment. FIG. 2 is a perspective view when firstside wall 57 of multi-function printer 11 shown in FIG. 1 is viewed fromfuser unit container 51 side. FIG. 3 is a perspective view when FIG. 2is cut at an approximately center position in a long-side direction ofheat roller 41. FIG. 4 is a perspective view when FIG. 3 is viewed fromthe lower portion of duct 53 side. FIG. 5 is a perspective view whenexhaust port 63 of first side wall 57 is viewed from the upper portionin a state where ceiling surface 71 of the duct is not shown. FIG. 6 isa perspective view of filter 65. FIG. 7 is a perspective view ofthru-beam type filter 85.

For example, multi-function printer 11 of the present embodimentincludes functions such as scanning, copying, or printing, form (fuses)a monochromatic or multicolor image on a sheet (for example, a recordingmaterial or a recording sheet) based on print job data input from anexternal device (for example, a personal computer (PC) (not shown)), anddischarges the sheet.

Multi-function printer 11 shown in FIG. 1 is configured to include atleast photosensitive drum 13, charging unit 15, developing roller 17,transfer roller 19, exposure device 21, fuser unit 23, sheet feedingcassette (not shown), sheet transport roller 25, sheet dischargingroller 27, and sheet discharging tray 29 in main body casing 31.

For example, one set of visible image forming units (process units) 33is disposed at an approximately center inside main body casing 31 ofmulti-function printer 11 shown in FIG. 1. For ease of explanation, forexample, it is described that one set of visible image forming units 33is disposed to form a black image in multi-function printer 11 shown inFIG. 1. However, the visible image forming unit having the similarconfiguration for each different color (yellow, magenta, cyan) may bedisposed.

Photosensitive drum 13 which has a role as an electrostatic latent imagecarrier according to print job data input into multi-function printer 11is provided in visible image forming unit 33, and charging unit 15,developing roller 17, transfer roller 19, and cleaning unit 35 aredisposed in the vicinity of photosensitive drum 13.

Charging unit 15 uniformly charges a predetermined potential (forexample, negative potential) on the surface of photosensitive drum 13.For example, preferably, charging unit 15 is a charge roller type whichcan uniformly charge the surface of photosensitive drum 13 withoutgenerating ozone as much as possible during charging with respect tophotosensitive drum 13. However, charging unit 15 is not limited to thecharge roller type, and for example, may use a contact type brush or anon-contact charger type.

Developing roller 17 develops electrostatic latent image formed onphotosensitive drum 13 by exposure device 21 described below using tonersupplied to developing roller 17. Accordingly, a toner imagecorresponding to the print job data is obtained. In the presentembodiment, for example, black toner is supplied to developing roller17. In multi-function printer 11, toner of each color may be supplied toeach developing roller of a visible image forming unit corresponding toeach color of yellow, magenta, and cyan, and having the sameconfiguration as visible image forming unit 33.

Transfer roller 19 is disposed to oppose photosensitive drum 13, andtransfers the toner image formed on the surface of photosensitive drum13 to sheet 37 which is transported along sheet transport path 45.Hereinafter, the toner image transferred to sheet 37 by transfer roller19 is referred to as an “unfused toner image”.

Cleaning unit 35 removes and recovers the toner which remains on thesurface of photosensitive drum 13 after the transfer processing isperformed in transfer roller 19.

Exposure device 21 includes a laser scanning unit (LSU) 39. Laserscanning unit 39 is configured to include a laser light source, apolygon mirror which performs scanning with the laser light emitted fromthe laser light source, a lens which introduces the laser light whichperforms the scanning by the polygon mirror into photosensitive drum 13,and a reflecting mirror. Laser scanning unit 39 exposes the surface ofphotosensitive drum 13 by the light from the polygon mirror according tothe input print job data, and forms the electrostatic latent imageaccording to the print job data on photosensitive drum 13.

Fuser unit 23 is configured to include heat roller 41 and pressureroller 43 which extend so as to be perpendicular to sheet 37. Heatroller 41 is heated to a predetermined target temperature (for example,fuse temperature within a range from 180° C. to 200° C.) by a heaterwhich is a heat source. Pressure roller 43 is biased toward heat roller41 by a spring (not shown). Fuser unit 23 heats and pressurizes sheet 37to which the toner image is transferred in pressure roller 43 and heatroller 41, and thus, the unfused toner image is fused on sheet 37.

Sheet transport path 45 is formed from a sheet feeding cassette (notshown) to sheet discharging tray 29 in main body casing 31. Sheettransport path 45 is configured of a transport path which passes throughfuser unit 23 from sheet transport roller 25 via a portion betweenphotosensitive drum 13 and transfer roller 19, and reaches sheetdischarging roller 27 (refer to an arrow A in FIG. 1). Sheet transportpath 45 becomes sheet discharging path 47 immediately before sheetdischarging roller 27. For example, a switchback transport path (notshown) for feeding sheet 37 to the position of transfer roller 19 againwhen a duplex printing is performed is provided in sheet dischargingpath 47.

A control portion (not shown) for integrally controlling all operationsof multi-function printer 11 is provided in main body casing 31. Thecontrol portion is configured using a processor (for example, CentralProcessing Unit (CPU), Micro Processing Unit (MPU), and Digital SignalProcessor (DSP)). The control portion controls each operation in eachportion of multi-function printer 11, that is, photosensitive drum 13,charging unit 15, developing roller 17, transfer roller 19, exposuredevice 21, fuser unit 23, sheet transport roller 25, and sheetdischarging roller 27. Control portion also controls the operation ofexhaust fan 49 (refer to FIG. 2) described below.

In multi-function printer 11 having the above-described configuration,an image forming process is performed as follows by control portion ofmulti-function printer 11.

When the image forming is performed, first, sheets 37 are dischargedfrom a sheet feeding cassette (not shown) to sheet transport path 45 oneby one using sheet transport roller 25.

After charging unit 15 uniformly charges the surface of photosensitivedrum 13, exposure device 21 exposes a charge region on the surface ofphotosensitive drum 13 by laser light according to the print job datainput from the external device. Accordingly, the electronic latent imagecorresponding to the print job data is formed on the surface ofphotosensitive drum 13. Continuously, developing roller 17 develops theelectronic latent image formed on the surface of the photosensitive drum13 using the toner supplied by developing roller 17. Accordingly, thetoner image corresponding to the print job data is obtained.

Transfer roller 19 transfers the toner image formed on the surface ofphotosensitive drum 13 to sheet 37 which is fed from the sheet feedingcassette (not shown) by sheet transport roller 25 and is transported.Accordingly, the unfused toner image corresponding to the print job datais transferred to sheet 37. The unfused toner image transferred to sheet37 is transported to fuser unit 23. Fuser unit 23 sufficiently heats andpressurizes the unfused toner image in heat roller 41 and pressureroller 43 and fuses the unfused toner image on sheet 37. Accordingly,the image corresponding to the print job data is formed on sheet 37, andsheet 37 is discharged to sheet discharging tray 29 by sheet dischargingroller 27.

Here, in multi-function printer 11 of the present embodiment, fuser unitcontainer 51 for accommodating fuser unit 23 is provided in the vicinityof fuser unit 23. Fuser unit container 51 is formed as a cavity whichhas airtightness on a level in which the ultrafine particles (UFP)generated inside fuser unit container 51, that is, in fuser unit 23 arenot leaked to the outside of fuser unit container 51.

More specifically, fuser unit container 51 is formed by connecting aplurality of metal plates and molding resin plates fixed to main bodycasing 31 to one another. Since fuser unit container 51 becomes anegative pressure by suction of exhaust fan 49 described below,existence of a small gap such as sheet transport path 45 communicatingwith the outside of the cavity is admitted. Outside air flows into fuserunit container 51 from the gap, and thus, fuser unit container 51 doesnot become a vacuum. An exclusive air feeding port may be provided infuser unit container 51.

Duct 53 is provided so as to be adjacent to fuser unit container 51.Duct 53 is formed in a long shape in a direction along axis 59 (refer toFIG. 2) of heat roller 41, and is disposed in the vicinity of fuser unit23 along axis 59 of heat roller 41. More specifically, duct 53 is formedin a long shape in the direction along axis 59 (refer to FIG. 2) of heatroller 41 with a portion of wall portion 55 in fuser unit container 51as first side wall 57. Exhaust fan 49 (refer to FIG. 2) is provided onone end side in a long-side direction of duct 53, and exhaust fan 49exhausts exhaust emissions including air existing in air transport space61 (refer to FIG. 1) of duct 53 to the outside of main body casing 31.

Exhaust port 63 (refer to FIG. 2) is opened to first side wall 57 offuser unit 23 side of duct 53, that is, first side wall 57 of wallportion 55 of fuser unit container 51. Exhaust port 63 causes fuser unit23 and duct 53 to communicate with each other. More specifically,exhaust port 63 causes fuser unit container 51 which is provided so asto cover fuser unit 23 and duct 53 to communicate with each other. Inthe present embodiment, as shown in FIG. 2, a plurality of (two in FIG.2) exhaust ports 63 are formed in the long-side direction of first sidewall 57. A gap between exhaust ports 63 and an opening area of eachexhaust port are set after container exhaust gas 87 described below isadjusted so as to be exhausted without variation in the long-sidedirection of fuser unit container 51.

Planar filter 65 is detachably attached to the inner wall surface ofduct 53 so as to be parallel with inner wall surface. The inner wallsurface of duct 53 is used as a collective name of ceiling surface 71,first side wall 57, second side wall 73, and bottom surface 75 of theduct. As shown in FIG. 6, in filter 65, filter main body 67 is heldinside frame body 69. Frame body 69 is held and removed with respect toa locking structure and a holding portion (not shown) such as a railprovided inside duct 53, and thus, filter 65 is attached to and detachedfrom duct 53.

In duct 53, a rectangular ceiling surface (ceiling surface 71 of theduct) of duct 53 in which the inner wall surface is along the long-sidedirection of duct 53 is formed. Filter 65 is attached to ceiling surface71 of the duct, and specifically, preferably, filter is installed in arectangular shape which covers ceiling surface 71 of the duct. As aresult, if filter 65 has an area which can cover almost the entireceiling surface 71 of the duct, filter 65 may be a single filter or aplurality of divided filters.

Filter 65 may be installed to cover all or a portion of first side wall57, second side wall 73, and bottom surface 75 in addition to ceilingsurface 71 of the duct. However, when filter 65 is provided on firstside wall 57, filter is provided on a portion other than exhaust port 63so that exhaust port 63 is not blocked.

Ceiling surface 71 of the duct is formed to be upwardly inclined so asto be heightened as ceiling surface 71 is away from exhaust port 63. Infirst side wall 57 and second side wall 73 opposing first side wallwhich are positioned in a state where ceiling surface 71 of the duct isinterposed therebetween, an included angle between first side wall 57and ceiling surface 71 and an included angle between second side wall 73and ceiling surface 71 become acute angles.

As shown in FIG. 6, the surface of filter 65 is configured so as to haveirregular surface 81 in which ditches 77 and convex portions 79 parallelwith each other to be extended in a direction inclined to the long-sidedirection of duct 53 are alternately disposed in the long-side direction(arrow B direction in FIG. 6) of ceiling surface 71 of the duct. Sincefilter 65 has irregular surface 81, the surface area is increased.

Ditch 77 and convex portion 79 configuring irregular surface 81 may beformed in various shapes. For example, although it is not shown, ditch77 may be formed in a V ditch, and convex portion 79 may be formed in aninverted V-shaped crest. Although it is not shown, in ditch 77 andconvex portion 79, a valley bottom of the V groove and an apex of theinverted-V shaped crest are curved, and a so-called waveform of a sinewave shape may be configured. Although it is not shown, ditch 77 andconvex portion 79 may be a recessed groove having a flat groove bottomand a protruding convex portion 79 having a flat apex.

In the present embodiment, thru-beam type filter 85 shown in FIGS. 5 and7 is attached so as to cover exhaust opening surface 83 (refer to FIG.2) of exhaust fan 49. As shown in FIG. 7, the surface of thru-beam typefilter 85 is also formed to have irregular surface 81 in which ditches77 and convex portions 79 parallel with each other are alternatelydisposed. Since thru-beam type filter 85 has irregular surface 81, thesurface area is increased. Thru-beam type filter 85 passes containerexhaust gas 87 (see below) which flows into via exhaust port 63. Similarto filter 65, thru-beam type filter 85 is also detachably attached toexhaust opening surface 83.

Next, an operation of multi-function printer 11 having theabove-described configuration will be described.

In multi-function printer 11, the unfused toner image corresponding tothe print job data input from the external device is transferred tosheet 37 and is transported to fuser unit 23. In fuser unit 23, sheet 37is held by heat roller 41 and pressure roller 43. The unfused tonerimage carried to sheet 37 becomes an image fused on sheet 37 and isfused by heating of heat roller 41 and pressurizing of pressure roller43.

At this time, in fuser unit 23, it is known that a very small quantityof toner configuring the unfused toner image is separated from theunfused toner image along water vapor according to vaporization of waterincluded in sheet 37. In general, the toner is configured of pigment,wax, and an external additive. A primary effect of the external additiveis to improve response efficiency between the external additive andstatic electricity, and for example, is used to attach minute particlessuch as silica on the toner surface. In recent years, there is a reportthat it is considered that the external additive particularly separatedalong with water vapor is one of factors increasing ultrafine particles(UFP) in multi-function printer 11.

In the present embodiment, the external additive separated from thetoner surface along with the water vapor generated during the fusing ofsheet 37 is carried to the upper portion of fuser unit container 51along with air which is moved by natural convection and a suction forceby exhaust fan 49. First side wall 57 which is a portion of wall portion55 is positioned on the upper portion of fuser unit container 51. Firstside wall 57 becomes a partition between duct 53 provided to be adjacentto fuser unit container 51 and first side wall. Duct 53 is formed in along shape in the direction along axis 59 of heat roller 41. That is,duct 53 is disposed to be adjacent in parallel with fuser unit 23 acrossthe partition, and thus, compactification of multi-function printer 11is realized. Exhaust port 63 is formed on first side wall 57 which isthe partition, and exhaust port 63 causes the inside of fuser unitcontainer 51, that is, an exposure space of fuser unit 23, and theinside (air transport space 61) of duct 53 to communicate with eachother.

In duct 53, the air of air transport space 61 flows toward one end sidein the long-side direction by exhaust fan 49 which is provided on oneend side in the long-side direction. Accordingly, the air inside fuserunit container 51 is sucked into and flows into air transport space 61of duct 53 which reaches a negative pressure via exhaust port 63. Theexternal additive (ultrafine particles: UFP) separated from the tonersurface along with the water vapor generated during the fusing of sheet37 is mostly included in suction air (hereinafter, referred to as“container exhaust gas”) along with other volatile organic compounds(VOC) and dust, and flows into air transport space 61 of duct 53.

When container exhaust gas 87 shown in FIGS. 2 and 3 is transferred toone end side in the long-side direction of duct 53, the containerexhaust gas comes into contact with the surface of planar filter 65which is attached in parallel with the inner wall surface of duct 53.Filter 65 and container exhaust gas 87 come into contact with eachother, and thus, it is confirmed that the ultrafine particles (UFP)included in container exhaust gas 87 are captured by filter 65.Specifically, it is possible to confirm the capturing of ultrafineparticles by measuring the amount of emission of the ultrafine particlesat the outlet side of exhaust fan 49 when filter 65 is provided in duct53 and when filter 65 is not provided in duct 53. It is considered thatthe reason why the ultrafine particles are captured by filter 65disposed in parallel with container exhaust gas 87 is because containerexhaust gas 87 becomes turbulent in the vicinity of the surface offilter 65 and as a result, a vortex is generated, and thus, theultrafine particles are caught on the surface of filter 65 andtherefore, are captured.

In filter 65, as the base material, vegetable fibers, mineral fibers,synthetic fibers, woven fabrics, non-woven fabrics, felts, webs, resinfoamed bodies, porous films, or the like may be used. Even when any basematerial is used, lots of minute voids, that is, fiber clearances andholes are formed on the surface of filter 65.

In a portion in which container exhaust gas 87 flowing to air transportspace 61 of duct 53 is far away from filter 65, the container exhaustgas uniformly flows and thus, a velocity gradient (velocity change) isnot generated. Meanwhile, since sliding is not generated on the surfaceof filter 65, flow velocities are continuously changed by influence of afriction force in the vicinity of filter 65, and a region in whichuniform flow is generated is formed. That is, a thin layer (boundarylayer) having a great velocity gradient is covered on the surface offilter 65. It is considered that the ultrafine particles, in whichtransport energy is decreased by the boundary layer and theabove-described vortex generated by the turbulence, are caught on minutevoids on the filter surface and are captured. The boundary layer ischanged by ultrafine particles (UFP) which are captured and deposited.It is considered that there are optimal values with respect to arelationship between the ultrafine particles (UFP) and the sizes of theminute voids, and the flow velocity of container exhaust gas 87.

In this way, in the present embodiment, since duct 53 is disposed in thevicinity of fuser unit 23 along axis 59 of heat roller 41, a wastefulspace is not generated in multi-function printer 11. As a result, theconfiguration itself of multi-function printer 11 becomes simple andcompact.

More specifically, in the present embodiment, duct 53 is also used as aportion of wall portion 55 of fuser unit container 51, and thus, it ispossible to easily manufacture multi-function printer 11. Since duct 53is disposed to be adjacent to fuser unit container 51 along (in parallelwith) heat roller 41 only across the partition, wasteful space is notgenerated in multi-function printer 11. As a result, the configurationitself of multi-function printer 11 becomes simple and compact. It isalso possible to easily replace filter 65, and thus, it is possible toimprove maintenance of multi-function printer 11.

Since filter 65 is configured in a long shape along the long-sidedirection of duct 53, a contact time between container exhaust gas 87and the filter is lengthened, probability of the ultrafine particles(UFP) being captured is increased, and it is possible to decrease theamounts of the ultrafine particles (UFP) exhausted to the outside ofmulti-function printer 11. Filter 65 does not cross air transport space61 of duct 53, and is installed in parallel with the transport directionof container exhaust gas 87 in air transport space 61. Accordingly,unlike the thru-beam type filter in the related art, filter 65 canprevent an increase of resistance when air is transported, and in otherwords, filter 65 can prevent an increase of output of the exhaust fan.

In multi-function printer 11, filter 65 is installed on ceiling surface71 of the duct, and thus, it is possible to allow container exhaust gas87 including the water vapor generated during the fusing of sheet 37 andultrafine particles (UFP) having buoyancy generated by ascending currentto effectively come into contact with filter 65. Particularly, sincecontainer exhaust gas 87 immediately after exhaust fan 49 is stopped ismoved at a low flow velocity in the vicinity of ceiling surface 71 ofthe duct and thereafter, the container exhaust gas stagnates, it ispossible to effectively capture the ultrafine particles (UFP).

In multi-function printer 11, ceiling surface 71 of the duct is formedto be upwardly inclined so as to be heightened as ceiling surface 71 isaway from exhaust port 63, and the included angle between second sidewall 73 and ceiling surface 71 of the duct becomes an acute angle.Accordingly, air transport space 61 interposed between second side wall73 and filter 65 becomes a corner space which is gradually narrowedtoward the upper portion. In the corner space, by friction forces ofsecond side wall 73 and filter 65, the flow velocity during the exhaustis gradually decreased toward the inner side which is the side remotefrom exhaust fan 49. It is assumed that container exhaust gas 87including the ultrafine particles (UFP) which moves upwardly along withthe water vapor ascends toward the corner space. Accordingly, it ispossible to deposit the ultrafine particles (UFP) on filter 65 from theinner side of the corner space. As a result, it is possible toeffectively use the surface of filter 65 from the inner side of thecorner space.

In multi-function printer 11, filter 65 having irregular surface 81 inwhich ditches 77 and convex portions 79 are alternately disposed isinstalled in the transport direction of container exhaust gas 87.Transported container exhaust gas 87 repeatedly collides with ditches 77and convex portions 79, and thus, a vortex is generated. Accordingly, infilter 65, it is possible to improve probability of the ultrafineparticles (UFP) being captured by minute voids of filter 65.

In multi-function printer 11, the plurality of exhaust ports 63 areprovided, and the gap and the area of each exhaust port 63 areappropriately set. Accordingly, compared to a case where one exhaustport 63 is provided, it is possible to suppress variation in an inflowamount of container exhaust gas 87 flowing in air transport space 61 ofduct 53 in the long-side direction of duct 53.

In multi-function printer 11, container exhaust gas 87 passes throughair transport space 61 of duct 53, and thus, container exhaust gas 87including the exhaust emissions from fuser unit 23 is exhausted fromexhaust opening surface 83 of exhaust fan 49 in a state where theultrafine particles (UFP) are decreased. At this time, container exhaustgas 87 including the exhaust emissions from fuser unit 23 passes throughthru-beam type filter 85, and thus, the remaining ultrafine particlesare captured again. Thru-beam type filter 85 is provided over the entirecross-section of duct 53, and thus, it is possible to capture ultrafineparticle secondarily. Filter 65 inside duct 53 and thru-beam type filter85 may be installed so that filter performance is appropriatelyadjusted. For example, a replacement period of filter 65 inside duct 53may be set to be lengthened, and a replacement period of thru-beam typefilter 85 may be set to be shortened.

Here, in the configuration of the related art in which filter 65 is notprovided in duct 53, the decrease of the ultrafine particles (UFP) isdependent on only thru-beam type filter 85. In this case, when thru-beamtype filter 85 is thickened to improve capture performance of ultrafineparticles (UFP), exhaust fan 49 having greater power is required, andthus, noise is also increased.

In contrast, in multi-function printer 11 of the present embodimentincluding filter 65 in duct 53, thru-beam type filter 85 may have anauxiliary performance. Accordingly, in multi-function printer 11 of thepresent embodiment, air resistance is not increased even when thru-beamtype filter 85 is attached, and it is possible to suppress an increasein the output of exhaust fan 49.

In filter 65, ditches 77 and convex portions 79 extend in the inclineddirection in the long-side direction of duct 53. As for the “inclinationin the long-side direction of duct 53”, two inclination directions areconsidered. One inclination direction is an inclination direction(separation inclination direction) in which the inclination end of oneend side (exhaust fan 49 side) in the long-side direction of the duct ofditch 77 and convex portion 79 positioned on ceiling surface 71 of theduct is away from first side wall 57. On the other hand, the otherinclination direction is an inclination direction (approach inclinationdirection) in which the inclination end of exhaust fan 49 side of ditch77 and convex portion 79 positioned on ceiling surface 71 of the ductapproaches first side wall 57.

Initially, container exhaust gas 87 flowing toward exhaust fan 49 in airtransport space 61 of duct 53 flows into duct 53 in a directionorthogonal to the long-side direction of duct 53 from exhaust port 63 offirst side wall 57. That is, the flow direction of container exhaust gas87 is gradually curved from exhaust port 63, and is converted into aperpendicular direction. Strictly speaking, the flow direction becomesthree-dimensional complicated flow lines which interfere with oneanother.

When ditches 77 and convex portions 79 are in the “separationinclination direction”, container exhaust gas 87 immediately after thecontainer exhaust gas flows from exhaust port 63 easily flows to thedownstream side without inversely flowing along the extension directionsof ditches 77 and convex portions 79. Accordingly, ditches 77 and convexportions 79 in the separation inclination direction easily come intocontact with container exhaust gas 87 over the entire length in theextension direction. As a result, in the separation inclinationdirection, the time when ditches 77 and convex portions 79 come intocontact with container exhaust gas 87 is lengthened.

Meanwhile, when ditches 77 and convex portions 79 are in the “approachinclination direction”, container exhaust gas 87 immediately after thecontainer exhaust gas flows from exhaust port 63 easily abuts the convexportions in a direction approximately orthogonal to the extensiondirection of convex portion 79. That is, container exhaust gas 87collides with convex portions 79, turbulence is easily generated, andnumerous vortexes are generated in the vicinity of filter 65. As aresult, in ditches 77 and convex portions 79 in the approach inclinationdirection, probability of the ultrafine particles being captured by theminute voids of filter 65 itself is improved.

Which of the approach inclination direction and the separationinclination direction can capture more ultrafine particles can beconfirmed by measuring the amounts of emission of the ultrafineparticles in the outlet side of exhaust fan 49. As a result of theconfirmation, it is understood that compared to the separationinclination direction, ditches 77 and convex portions 79 in the approachinclination direction increase efficiency of capturing the ultrafineparticles.

As shown in FIG. 8, the surface of filter 65 may be formed to includeirregular surface 81 on which ditches 77 and convex portions 79extending in parallel with the long-side direction of duct 53 arealternately disposed in the short-side direction (a directionperpendicular to an arrow B of FIG. 8) of ceiling surface 71 of theduct. Also in this case, since filter 65 includes irregular surface 81,the surface area is increased. In FIG. 8, the same reference numeralsare assigned to the same configurations as FIG. 6 and are described.

In the above-described configuration, since the duct is disposed in thevicinity of the fuser unit along the axis of the heat roller, a wastefulspace is not generated in an image forming apparatus. As a result, theconfiguration itself of the image forming apparatus becomes simple andcompact. It is also possible to easily replace the filter, and thus, itis possible to improve the maintenance of the image forming apparatus.

Since the filter is configured in a long shape along the long-sidedirection of the duct, a contact time between the exhaust gas and thefilter is lengthened, the probability of the ultrafine particles beingcaptured is improved, and it is possible to decrease the amounts of theultrafine particles exhausted to the outside of the image formingapparatus. Since the filter does not cross air transport space of theduct, unlike the thru-beam type filter in the related art, the filtercan prevent an increase of resistance when air is transported, and inother words, the filter can prevent the increase in the output of theexhaust fan.

The duct is also used as a portion of the wall portion of the fuser unitcontainer, and thus, it is possible to easily manufacture the imageforming apparatus. Since the duct is disposed to be adjacent to thefuser unit container along the pressure roller, wasteful space is notgenerated in the image forming apparatus. As a result, the configurationitself of the image forming apparatus becomes simple and compact. It isalso possible to easily replace filter, and thus, it is possible toimprove the maintenance of the image forming apparatus.

The planar filter is attached so as to be parallel with the inner wallsurface of the duct. Since the filter is disposed so as to be parallelwith the inner wall surface, it is possible to easily perform directfixation with respect to the inner wall surface using a bonding agent, adouble-sided adhesive tape, or the like. In the duct, since the filteris directly fixed to the inner wall surface, a decrease in the airtransport space is suppressed to the minimum.

The filter is installed so as to be parallel with the ceiling surface ofthe duct, and thus, it is possible to allow the exhaust gas includingthe water vapor generated during the fusing of the sheet and ultrafineparticles having buoyancy generated by the ascending current toeffectively come into contact with the filter. Particularly, since theexhaust gas immediately after the exhaust fan is stopped is moved at alow flow velocity in the vicinity of the ceiling surface and thereafter,the exhaust gas stagnates, it is possible to effectively capture theultrafine particles.

In the above-described configuration, the plurality of exhaust ports areprovided, and the gap and the area of each exhaust port areappropriately set, and thus, compared to the case where one exhaust portis provided, it is possible to suppress variation in the inflow amountof the exhaust gas flowing in the air transport space of the duct in thelong-side direction of the duct.

In the above-described configuration, the exhaust gas passes through theair transport space of the duct, and thus, the exhaust gas including theexhaust emissions from the fuser unit is exhausted from the exhaustopening surface of the exhaust fan in the state where the ultrafineparticles are decreased. At this time, the exhaust gas passes throughthe thru-beam type filter, and thus, the remaining ultrafine particlesare captured again. The thru-beam type filter is provided over theentire cross-section of the duct, and thus, it is possible to captureultrafine particles secondarily.

As described above, various embodiments are described with reference tothe drawings. However, it goes without saying that the present inventionis not limited to the examples. It is clear to a person skilled in theart that various modifications and corrections may be applied within ascope described in claims, and various modifications and corrections areincluded in the technical range of the present invention.

According to the present invention, the present invention is useful asthe image forming apparatus which decreases the amount of emission ofthe ultrafine particles and suppresses the increase in the output of theexhaust fan by the simple structure.

What is claimed is:
 1. An image forming apparatus comprising: a fuserunit which includes a heat roller and a pressure roller which heat andpressurize a sheet on which an unfused toner image is carried and fusethe unfused toner image on the sheet; a duct which is formed in adirection along an axis of the heat roller and is disposed along theaxis of the heat roller; an exhaust fan which exhausts the duct; anexhaust port which is opened to a first side wall of the fuser unit sideof the duct and causes the fuser unit and the duct to communicate witheach other; and a planar filter which is attached to an inner wallsurface of the duct, wherein a surface of the filter is an irregularsurface in which ditches and convex portions extending in a directioninclined to a long-side direction of the duct are alternately disposedin the long-side direction of the duct.
 2. The imaging forming apparatusof claim 1, further comprising a fuser unit container which accommodatesthe fuser unit, wherein the first side wall is a portion of a wallportion in the fuser unit container.
 3. The imaging forming apparatus ofclaim 1, wherein the planar filter is stuck to an inner wall surface ofthe duct so as to be parallel with the inner wall surface.
 4. Theimaging forming apparatus of claim 1, wherein the planar filter isattached to a ceiling surface inside the duct so as to be parallel withthe ceiling surface.
 5. The imaging forming apparatus of claim 1,wherein the surface of the filter is an irregular surface on which theditches and convex portions extended so as to be orthogonal to thelong-side direction of the duct are alternately disposed in a long-sidedirection of a ceiling surface of the duct.
 6. The imaging formingapparatus of claim 1, wherein the surface of the filter is an irregularsurface on which the ditches and convex portions extending in adirection inclined to the long-side direction of the duct arealternately disposed in a long-side direction of a ceiling surface ofthe duct.
 7. The imaging forming apparatus of claim 1, wherein thesurface of the filter is an irregular surface on which the ditches andthe convex portions extended so as to be parallel to the long-sidedirection of the duct are alternately disposed in a short-side directionof a ceiling surface of the duct.
 8. The imaging forming apparatus ofclaim 1, wherein a plurality of the exhaust ports are formed in along-side direction of the first side wall.
 9. The imaging formingapparatus of claim 1, wherein a thru-beam type filter which passesexhaust emission from the fuser unit is attached to an exhaust openingsurface of the exhaust fan.
 10. An image forming apparatus comprising: afuser unit which includes a heat roller and a pressure roller which heatand pressurize a sheet on which an unfused toner image is carried andfuse the unfused toner image on the sheet; a duct which is formed in along shape in a direction along an axis of the heat roller and isdisposed along the axis of the heat roller; an exhaust fan whichexhausts the duct; an exhaust port which is opened to a first side wallof the fuser unit side of the duct and causes the fuser unit and theduct to communicate with each other; and a planar filter which isattached to an inner wall surface of the duct, wherein a surface of thefilter is an irregular surface on which ditches and convex portionsextended so as to be parallel to a long-side direction of the duct arealternately disposed in a short-side direction of the duct.